Introduce a channel FundingScope

When establishing a channel, the funding transaction may be replaced
either:
- after the funding transaction has confirmed using splicing,
- before the funding transaction has confirmed for v2 channel
  establishment using tx_init_rbf, or
- before the splice's funding transaction has confirmed using
  tx_init_rbf.

In each of these cases, fields in ChannelContext will need to be updated
once the funding transaction confirms. Additionally, the same fields for
a pending attempt may need to be considered instead of a previously
confirmed funding.

This commit introduces a FundingScope to hold the aforementioned fields.
It lives next to ChannelContext and will be needed whenever these fields
are accessed. The next few commits will move the relevant fields to
FundingScope and provide access to them whenever needed, allowing to
swap in another FundingScope when necessary.

Author: jkczyz

lightning/src/ln/channel.rs

@@ -1522,6 +1522,12 @@ impl UnfundedChannelContext {
 	}
 }
 
+/// Information pertaining to an attempt at funding the channel. This is typically constructed
+/// during channel establishment and may be replaced during channel splicing or if the attempted
+/// funding transaction is replaced using tx_init_rbf.
+pub(super) struct FundingScope {
+}
+
 /// Contains everything about the channel including state, and various flags.
 pub(super) struct ChannelContext<SP: Deref> where SP::Target: SignerProvider {
 	config: LegacyChannelConfig,
@@ -2166,6 +2172,7 @@ impl<SP: Deref> PendingV2Channel<SP> where SP::Target: SignerProvider {
 		match self.unfunded_context.holder_commitment_point {
 			Some(holder_commitment_point) => {
 				let funded_chan = FundedChannel {
+					funding: self.funding,
 					context: self.context,
 					interactive_tx_signing_session: Some(signing_session),
 					holder_commitment_point,
@@ -2203,7 +2210,7 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
 		msg_channel_reserve_satoshis: u64,
 		msg_push_msat: u64,
 		open_channel_fields: msgs::CommonOpenChannelFields,
-	) -> Result<ChannelContext<SP>, ChannelError>
+	) -> Result<(FundingScope, ChannelContext<SP>), ChannelError>
 		where
 			ES::Target: EntropySource,
 			F::Target: FeeEstimator,
@@ -2377,6 +2384,8 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
 
 		// TODO(dual_funding): Checks for `funding_feerate_sat_per_1000_weight`?
 
+		let funding = FundingScope {
+		};
 		let channel_context = ChannelContext {
 			user_id,
 
@@ -2521,7 +2530,7 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
 			next_funding_txid: None,
 		};
 
-		Ok(channel_context)
+		Ok((funding, channel_context))
 	}
 
 	fn new_for_outbound_channel<'a, ES: Deref, F: Deref, L: Deref>(
@@ -2542,7 +2551,7 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
 		holder_signer: <SP::Target as SignerProvider>::EcdsaSigner,
 		pubkeys: ChannelPublicKeys,
 		_logger: L,
-	) -> Result<ChannelContext<SP>, APIError>
+	) -> Result<(FundingScope, ChannelContext<SP>), APIError>
 		where
 			ES::Target: EntropySource,
 			F::Target: FeeEstimator,
@@ -2608,7 +2617,9 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
 
 		let temporary_channel_id = temporary_channel_id.unwrap_or_else(|| ChannelId::temporary_from_entropy_source(entropy_source));
 
-		Ok(Self {
+		let funding = FundingScope {
+		};
+		let channel_context = Self {
 			user_id,
 
 			config: LegacyChannelConfig {
@@ -2746,7 +2757,9 @@ impl<SP: Deref> ChannelContext<SP> where SP::Target: SignerProvider {
 			local_initiated_shutdown: None,
 			is_manual_broadcast: false,
 			next_funding_txid: None,
-		})
+		};
+
+		Ok((funding, channel_context))
 	}
 
 	pub(crate) fn get_value_to_self_msat(&self) -> u64 {self.value_to_self_msat}
@@ -4502,6 +4515,7 @@ pub(super) struct DualFundingChannelContext {
 // Holder designates channel data owned for the benefit of the user client.
 // Counterparty designates channel data owned by the another channel participant entity.
 pub(super) struct FundedChannel<SP: Deref> where SP::Target: SignerProvider {
+	pub funding: FundingScope,
 	pub context: ChannelContext<SP>,
 	pub interactive_tx_signing_session: Option<InteractiveTxSigningSession>,
 	holder_commitment_point: HolderCommitmentPoint,
@@ -8518,6 +8532,7 @@ impl<SP: Deref> FundedChannel<SP> where
 
 /// A not-yet-funded outbound (from holder) channel using V1 channel establishment.
 pub(super) struct OutboundV1Channel<SP: Deref> where SP::Target: SignerProvider {
+	pub funding: FundingScope,
 	pub context: ChannelContext<SP>,
 	pub unfunded_context: UnfundedChannelContext,
 	/// We tried to send an `open_channel` message but our commitment point wasn't ready.
@@ -8549,7 +8564,7 @@ impl<SP: Deref> OutboundV1Channel<SP> where SP::Target: SignerProvider {
 		let holder_signer = signer_provider.derive_channel_signer(channel_value_satoshis, channel_keys_id);
 		let pubkeys = holder_signer.pubkeys().clone();
 
-		let context = ChannelContext::new_for_outbound_channel(
+		let (funding, context) = ChannelContext::new_for_outbound_channel(
 			fee_estimator,
 			entropy_source,
 			signer_provider,
@@ -8575,7 +8590,7 @@ impl<SP: Deref> OutboundV1Channel<SP> where SP::Target: SignerProvider {
 
 		// We initialize `signer_pending_open_channel` to false, and leave setting the flag
 		// for when we try to generate the open_channel message.
-		let chan = Self { context, unfunded_context, signer_pending_open_channel: false };
+		let chan = Self { funding, context, unfunded_context, signer_pending_open_channel: false };
 		Ok(chan)
 	}
 
@@ -8775,6 +8790,7 @@ impl<SP: Deref> OutboundV1Channel<SP> where SP::Target: SignerProvider {
 		log_info!(logger, "Received funding_signed from peer for channel {}", &self.context.channel_id());
 
 		let mut channel = FundedChannel {
+			funding: self.funding,
 			context: self.context,
 			interactive_tx_signing_session: None,
 			holder_commitment_point,
@@ -8815,6 +8831,7 @@ impl<SP: Deref> OutboundV1Channel<SP> where SP::Target: SignerProvider {
 
 /// A not-yet-funded inbound (from counterparty) channel using V1 channel establishment.
 pub(super) struct InboundV1Channel<SP: Deref> where SP::Target: SignerProvider {
+	pub funding: FundingScope,
 	pub context: ChannelContext<SP>,
 	pub unfunded_context: UnfundedChannelContext,
 	pub signer_pending_accept_channel: bool,
@@ -8883,7 +8900,7 @@ impl<SP: Deref> InboundV1Channel<SP> where SP::Target: SignerProvider {
 			htlc_basepoint: HtlcBasepoint::from(msg.common_fields.htlc_basepoint)
 		};
 
-		let context = ChannelContext::new_for_inbound_channel(
+		let (funding, context) = ChannelContext::new_for_inbound_channel(
 			fee_estimator,
 			entropy_source,
 			signer_provider,
@@ -8907,7 +8924,7 @@ impl<SP: Deref> InboundV1Channel<SP> where SP::Target: SignerProvider {
 			unfunded_channel_age_ticks: 0,
 			holder_commitment_point: HolderCommitmentPoint::new(&context.holder_signer, &context.secp_ctx),
 		};
-		let chan = Self { context, unfunded_context, signer_pending_accept_channel: false };
+		let chan = Self { funding, context, unfunded_context, signer_pending_accept_channel: false };
 		Ok(chan)
 	}
 
@@ -9040,6 +9057,7 @@ impl<SP: Deref> InboundV1Channel<SP> where SP::Target: SignerProvider {
 		// Promote the channel to a full-fledged one now that we have updated the state and have a
 		// `ChannelMonitor`.
 		let mut channel = FundedChannel {
+			funding: self.funding,
 			context: self.context,
 			interactive_tx_signing_session: None,
 			holder_commitment_point,
@@ -9073,6 +9091,7 @@ impl<SP: Deref> InboundV1Channel<SP> where SP::Target: SignerProvider {
 
 // A not-yet-funded channel using V2 channel establishment.
 pub(super) struct PendingV2Channel<SP: Deref> where SP::Target: SignerProvider {
+	pub funding: FundingScope,
 	pub context: ChannelContext<SP>,
 	pub unfunded_context: UnfundedChannelContext,
 	pub dual_funding_context: DualFundingChannelContext,
@@ -9109,7 +9128,7 @@ impl<SP: Deref> PendingV2Channel<SP> where SP::Target: SignerProvider {
 					"Provided current chain height of {} doesn't make sense for a height-based timelock for the funding transaction",
 					current_chain_height) })?;
 
-		let context = ChannelContext::new_for_outbound_channel(
+		let (funding, context) = ChannelContext::new_for_outbound_channel(
 			fee_estimator,
 			entropy_source,
 			signer_provider,
@@ -9133,6 +9152,7 @@ impl<SP: Deref> PendingV2Channel<SP> where SP::Target: SignerProvider {
 			holder_commitment_point: HolderCommitmentPoint::new(&context.holder_signer, &context.secp_ctx),
 		};
 		let chan = Self {
+			funding,
 			context,
 			unfunded_context,
 			dual_funding_context: DualFundingChannelContext {
@@ -9255,7 +9275,7 @@ impl<SP: Deref> PendingV2Channel<SP> where SP::Target: SignerProvider {
 			htlc_basepoint: HtlcBasepoint(msg.common_fields.htlc_basepoint)
 		};
 
-		let mut context = ChannelContext::new_for_inbound_channel(
+		let (funding, mut context) = ChannelContext::new_for_inbound_channel(
 			fee_estimator,
 			entropy_source,
 			signer_provider,
@@ -9311,6 +9331,7 @@ impl<SP: Deref> PendingV2Channel<SP> where SP::Target: SignerProvider {
 			holder_commitment_point: HolderCommitmentPoint::new(&context.holder_signer, &context.secp_ctx),
 		};
 		Ok(Self {
+			funding,
 			context,
 			dual_funding_context,
 			interactive_tx_constructor,
@@ -10284,6 +10305,8 @@ impl<'a, 'b, 'c, ES: Deref, SP: Deref> ReadableArgs<(&'a ES, &'b SP, u32, &'c Ch
 		};
 
 		Ok(FundedChannel {
+			funding: FundingScope {
+			},
 			context: ChannelContext {
 				user_id,